HST Emission-Line Galaxies at z ~ 2: The Mystery of Neon
Abstract
We used two near-IR grism surveys (AGHAST and 3DHST) from the Hubble Space Telescope to examine the strength of [Ne III] 3869 relative to H-beta, [O II] 3727 and [O III] 5007 in 236 low mass (7.5 < log(Mstar/Msolar) < 10.5) star-forming galaxies in the redshift range 1.90 < z < 2.35. By stacking the data by stellar mass, we showed that the [Ne~III]/[O~III] ratios of the z ~ 2 universe are enhanced by ~0.2 dex more than those seen in a comparable set of local SDSS galaxies. We considered possible explanations for this 4-sigma result, including higher oxygen depletion out of the gas-phase, denser H II regions, and the existence of a larger population of X-ray obscured AGN at z ~ 2 compared to z ~ 0. None of these simple scenarios, alone, are favored to explain the observed line ratios.
- Publication:
-
American Astronomical Society Meeting Abstracts #225
- Pub Date:
- January 2015
- Bibcode:
- 2015AAS...22520604Z